Plastic materials are easily to form, can be inexpensively produced, have good resistance against the chemicals, and, besides, are rich in softness and flexibility, and have, therefore, been used for a variety of applications and, specifically, for daily necessaries and for packing materials.
In recent years, there have been developed highly functional materials improving surface properties such as wettability and the like. Viscous contents tend to adhere onto the inner surfaces of the packing materials. To solve this problem, the following documents are disclosing the materials that are newly developed having surface properties that work to keep the contents from adhering or enable the contents to slide down.
Patent documents 1 and 2 are disclosing packing materials such as containers and lids having surfaces (inner surfaces) on which hydrophobic fine oxide particles (e.g. , hydrophobic silica) are deposited having an average primary particle diameter of 3 to 100 nm and a BET specific surface area of 50 to 300 m2/g. These packing materials have such surface properties that the water-containing substances such as yogurt and the like adhere thereto difficultly.
A patent document 3 is proposing a lid of which the surface is coated with a water-repelling film of a structure formed by dispersing or depositing fine oxide particles having an average particle diameter of 5 nm to 100 nm on the surface of a resin film formed by using resin particles of an average particle diameter of 1 to 20 μm.
According to the arts proposed in the patent documents 1 and 2, the surface to which the content comes in contact is formed to be finely rugged, fine oxide particles are deposited on the finely rugged surface so as to express water-repelling property (hydrophobic property) , and property that do not adhere to the water-containing substances is expressed by the hydrophobic property.
The above arts are satisfactory in regard to the property of not adhering to the water-containing substances but are still unsatisfactory in regard to sliding property (slide-down property). Therefore, further improvements are necessary concerning the property for sliding down viscous water-containing substances.
Further, a patent document 4 is proposing a bottle of a multilayer structure including an innermost layer of an olefin resin that has an MFR (melt flow rate) of not less than 10 g/10 min.
The innermost layer of this multilayered bottle has excellent wettability for the oily content. Therefore, if the bottle is inverted or tilted, the oily content such as mayonnaise or the like falls down spreading along the surface of the innermost layer and is thoroughly discharged without adhering or remaining on the inner wall surface (innermost layer surface) of the bottle.
As for the bottles for containing viscous non-oily contents in which plant fibers are dispersed in water like ketchup, a patent document 5 and a patent document 6 are disclosing polyolefin resin bottles having an innermost layer which is blended with a saturated or unsaturated aliphatic amide as a lubricating agent.
The above patent documents 4 to 6 are all trying to improve sliding property of the plastic containers for the contents by suitably selecting the kind of the thermoplastic resin that forms the inner surfaces of the containers and the lubricating agent that is added to the resin, and are achieving improvements in the sliding property to some extent. However, limitation is imposed on improving the sliding property, and striking improvement has not been, achieved yet.
According to the above arts, further, the fine oxide particles must be deposited on the surfaces involving a difficulty in that the arts cannot be applied to the containers in the form of, specifically, bottles. This is because with the containers such as blow-formed bottles as representatively formed by stretch-forming, the mouth portion is so narrow that it is difficult to deposit, by blowing, a liquid in which fine oxide particles are dispersed on the inner surfaces of the containers.
It can be, further, contrived to disperse fine oxide particles in a resin that forms the surface, and form the resin into the shape of a bottle so that the fine oxide particles are distributed in the inner surface of the bottle. According to the study by the present inventors, however, it has been confirmed that the fine oxide particles must be dispersed in large amounts to realize the slide-down property to a certain degree.